To improve environmental quality for living beings, exposure to polluting substances is an issue. Typically, for polluting substances maximum exposure concentrations have been established.
In ambient air, substances such as NO (nitrogen monoxide), NO2 (nitrogen dioxide), SO2 (sulphur dioxide), CO (carbon monoxide) are considered as polluting and posing a health risk to living beings or serve as indicator for other types of pollutants.
To monitor these substances various methods exist.
For example, for NO2 monitoring and measurement, passive sampling is known. This sampling method involves exposing a diffusion tube comprising a NO2 absorbing reactant to ambient air for a predetermined time. During exposure the NO2 absorbing reactant absorbs NO2, which creates reaction products in the reactant. After exposure the NO2 absorbing reactant is analyzed to determine presence and amount of the reaction products as a measure for the concentration of NO2 during the exposure. A well known type of a passive sampler is the Palmes tube which is based on triethanolamine (TEA) as NO2 absorber.
Passive sampling may involve low costs, but the method is relatively time consuming and has long integration times.
Also, real time monitoring devices are commercially available that are based on electrochemical cells. Such cells comprise electrode and counter electrode pairs in which the electrode and counter electrode are separated by an electrolyte-based medium. Presence of the targeted polluting substance in the electrochemical cell will influence the electrochemical potential in the electrochemical cell. The electrochemical potential is typically proportional to the concentration of the targeted polluting substance.
Use of electrochemical cells in monitoring polluting substances allows in principle for (almost) real time detection and analysis. However, electrochemical cells of this type are known to be sensitive to variations of the humidity of the gas volume being analyzed. Additionally, the sensitivity for a particular gas species may be affected by other interfering gas species in the measured gas volume (cross-sensitivity). Such cross-sensitivity may vary as a function of concentration of the interfering gas species and the combinations of these species. Both humidity and cross-sensitivity effects are adverse to the reproducibility of measurements by thus type of electrochemical cell devices.
To reduce the cross-sensitivity, additional correction by computational models is available. The computational models are based on measurements of the interfering gas species (and combinations thereof) that typically suffer from a similar cross-sensitivity effect. This type of correction is computationally intensive and adds largely to the costs of this type of device.
It is an object of the present invention to overcome or mitigate the disadvantages of the prior art.